skip rollup and use babel only as rollup is not packaged

--- a/package.json
+++ b/package.json
@@ -2,7 +2,7 @@
   "name": "vue",
   "version": "2.4.2",
   "description": "Reactive, component-oriented view layer for modern web interfaces.",
-  "main": "dist/vue.runtime.common.js",
+  "main": "lib/compiler/index.js",
   "module": "dist/vue.runtime.esm.js",
   "unpkg": "dist/vue.js",
   "typings": "types/index.d.ts",